Process for removing electrolytes from aqueous solution

ABSTRACT

A process for removing electrolytic substances from water which comprises electrodialyzing an aqueous solution containing electrolytic substances using an ion-exchange membrane to remove the electrolytic substances from the aqueous solution, such exchange membrance consisting of an insoluble, infusible synthetic organic polymer having dissociable ionic groups chemically bonded thereto and having pores through which ions can pass the membrane, at least one substantial surface of the ionexchange membrane intimately retaining an electrolytic substance having an opposite electric charge to the charge of the ionexchange group of the ion-exchange membrane and being incapable of passing through the pores of the ion-exchange membrane.

United States Patent ,[191

Mizutani et" al.

[ Jan. 8, 1974 PROCESS FOR REMOVING 3,276,990 10/1966 Hanl et a1. 204/296 L CT L O AQUEOUS 3,276,991 10/1966 I l-lani et a1. 204/296 MiZUtflnl et a1. P 3,510,418 5/1970 Mizutani et a1. 204/180 P X [75] Inventors: Yukio Mizutani; Toshikatsu Sata, 3,654,125 4/1972 Leitz 204/301 both Tokuyama; Izuo 3,677,923 7/1972 B161 204/180 P Kudamatsu, a1l of Japan; Reiichi I V Y m d d, l t f Primary Examiner-John H. Mack Tokuyama, Japan by Masako Assistant Examiner-14. C. Prescott I Y hi Attorney-Sherman and Shalloway [73] Assignee: Tokuyama Soda Kabushiki Kaisha, 57] ABSTRACT Tokuyama-shl, Yamaguehl-ken,

Japan A process for removing electrolytic substances from water which comprises 'electrodlialyzing an aqueous Filedl qfl- 13, 1971 solution containing electrolytic substances using an [21] d 179-9992 ion-exchange membrane to remove the electrolytic substances from the aqueous solution, such exchange l membrance consisting of an insoluble, infu'sible synt Applicafifill Priority Data thetic organic polymer having dissociable ionic groups Sept. 14, 1970 Japan 45-79992/70 chemically bonded thereto and having pores through which ions can pass the-membrane, at least one sub [52] 05. C1,, 204/180 P, 204/301 stantial surface of the ion-exchange membrane inti- [51] Int, Cl B013 13/02 mately retaining an electrolytic substance having an [58] Field of Search 204/180 P, 301 opposite electric charge to the charge of the ionexchange group of the ion-exchange membrane and [56] References Cited being incapable of passing through the pores of the I UNITED STATES PATENTS ion-exchangem'embrane. 3,276,989 10/1966 Nishihara et a1 .f. 204/296 4 Claims, 2 Drawing Figures PAIENIEDJIIII 8 I974 I 3.784.457

w A E & Lu .J o m G v Lu 5 (f) 3*: a

o w c: 3 C 5 5 g LU No4I 0 60 I20 I80 RUNNING TIME OF ELECTRODIALYSIS (MINUTE) 2 LL] 5 g Fl 2 IJJJ 05 mo 3 0.4 No.4 i a U) 2% a 0 m0: 0 P I I I 5 0 60 I20 I I80 9 LU RUNNING TIME OF ELECTRODIALYSIS (MINUTE) PROCESS FOR REMOVING ELECTROLYTES FROM AQUEOUS SOLUTION This invention relates to a process for removing electrolytes from water by the electrodialysis method using an ion-exchange membrane which comprises removing electrolytic substances from an aqueous solution containing such electrolytic substances to thereby give.

water containing the electrolytic substances in lower concentrations, preferably water suited for agricultural, industrial or drinking purposes.

Generally, the contents of salts allowed for potable water are up to about 500 ppm, and in the production of potable water now being practiced, attempts are made to reduce the contents of salts to l200 ppm or below. Industrial water, too, requires high quality similar to that of potable water according to a particular use, for instance when used as cooling water for rolling steels. Therefore, except for some special instances, industrial water should also contain as little salts as possible in order to exhibit goods results in a specific use.

age of water for household, agricultural and industrial.

uses has been seriously considered. Studies have been made, therefore, as to a process for producing water for drinking and industrial uses by removing salts from sea water, lake water, river water, underground water, and other aqueous solutions containing the salts in high concentrations, or a process. for regenerating waste water or sewage water which has been used once. One advantageous procedure has emerged from the studies, in which the salts are removed by electrodialysis using an ion-exchange membrane, and has attracted atten' tion. 7

Natural river or lake water, however, contains organic matter such as humic acid. There is also the discarding of detergents in rivers or lakes, and recently, the river or lake water usually contains organic matter in a concentration of several to several hundred ppm or above. Likewise, industrial waste matter frequently contains various organic, ionic substances. For example, the pulp spent liquor contains ligninsulfonic acid of low molecular weight and also acetic acid. Furthermore, in the processing of foodstuffs, acids, salts or bases may be required to be removed from aqueous solutions containing organic matters, for example the re- 'moval of acids from fruit juices, or the removal of salts of milk.

When such river water or waste water is electrodialyzed using an ion-exchange membrane, organic substances such as detergents or low molecular weight ligninsulfonic acids adhere to the ion-exchange membrane, and deteriorate the excellent quality of ionexchange membrane. Typical deteriorating phenomena are: the electrical resistance of the ion-exchange membrane increases exceedingly and as a result, electric power unit increases remarkably; due to the so-called neutrality disturbing phenomenon which causes changes in pH of feed water and concentrated solution, the alkaline earth metal salts contained in the aqueous solution deposit on the surface of the ion-exchange membrane as'carbonates or hydroxides, which maylead to complete failure of electrodialysis; or the current efficiency is decreased.

An object of the present invention is to provide a process for removing electrolytic substances from water solutions containing the electrolytic substances by the electrodialysis method using an ion-exchange membrane, in which the removal of the electrolytic substances can be performed efficiently without undesirable phenomena such as the increased electrical resistance of the electrodialysis system, the neutrality disturbing phenomenon, or the reduction in current efficiency, even when some organic matters detrimental to electrodialysis are present in the aqueous solution.

Other objects of the invention will become apparent from the following description.

According to the present invention, a process is provided for removing electrolytic substances from water which comprises electrodialyzing an aqueous solution containing electrolytic substances using an ionexchange membrane to remove the electrolytic substances from the aqueous solution, said exchange membrane consisting of an insoluble, infusible synthetic organic polymer having dissociable ionic groups chemically bonded thereto and, having pores through which ions permeate, at least one substantial surface of the ion-exchange membrane intimately retaining an electrolytic substance having an opposite electric charge to the charge of the ion-exchange group of the ionexchange membrane and being incapable of passing through the pores of the ion-exchange membrane.

tail.

In the accompanying drawings:

FIG. 1 is a graphic representation showing the changes of voltage with time in Referential Example, and l FIG. 2 is a graphic representation showing the changes of voltage with time in Example 1.

A thorough investigation was made concerning the deposition of ionic organic matters on the ionexchange membrane and its marked reduction of the function of the ion-exchange membrane as described above. As a result, it was found that the ionic organic matters are mainly anionic or cationic substances having a molecular weight of about to 300, and that these ionic substances not only deposit on the surface of the ion-exchange membrane but also partly permeate through pores of the ion exchange membrane, which in turn may cause the blockage of pores, or in some case, render the bipolar ion-exchange membrane.

to cause polarization, making it difficult for the electrolytic ions to move. It has also been found that ionic substances having lower molecular weights, such as acetic acid, can pass through the pores of the ion-exchange membrane easily, and thus do not cause serious troubles. Furthermore, it has been found that substances having larger molecular weights may deposit on the surface of the ion-exchange membrane, but cannot pass through the "pores because of large sizes, thus hardly giving any trouble.

The process of the present invention is based on the above-described new findings, and the critical feature of the present invention is that electrodialysis is performed using an ion-exchange membrane having been The invention will be described below in further demany cases, this membranous polymeric substance has a cross-linked structure, and it is of a structure having pores through which ions permeate. The ion-exchange membrane used in the present invention is characteristic in that its surface and a very shallow inner portion containing the surface (in the present specification and claims, these will be generically termed substantial surface) have been modified with a specific treating agent so that the substantial surface intimately retains an electrolytic substance having an opposite electric charge to the charge of the ion-exchange membrane and being incapable of passing through the pores of the ion-exchange membrane. The term the substantial surface of the ion-exchange membrane intimately retains the electrolytic substance means that either the electrolytic substance is strongly adsorbed to the surface mainly by an electrostatic force, or it is chemically bonded to the surface by a covalent bond.

That the electrolytic substance having anopposite electric charge to the charge of the ion-exchange membrane used in the present invention should not pass the pres of the ion-exchange membrane is one of the important requirements of the present invention. Specific conditions for realizing this requisite somewhat differ depending upon whether the electrolytic substance is adsorbed to the substantial surface of the ion-exchange membrane or whether it is chemically bonded to the substantial surface by a covalent bond. Where the electrolytic substance is intimately maintained by adsorption, the molecular weight of the electrolytic substance is of utmost importance, and the essential requirement for the electrolytic substance not to enter the pores is that the molecular weight of the electrolytic substance should be at least 400, preferably above 1000. On the other hand, when the electrolytic substance is maintained intimately'by the ion-exchangemembrane by a covalent bond, the electrolytic substance is integrated with the membranous polymer and the whole constitutes macromolecules. Since the electrolytic substance is completely restrained by this from free movement, even if the electrolytic substance has a low molecular weight, the electrolytic substance never permeates through the pores of the ion-exchange membrane. Accordingly, it will be understood that in the latter case, no limitation as to the molecular weight is necessary. The amount of the electrolytic substance to be present on the substantial surface of the ion-exchange membrane should be at least sufficient for the electric charge of the electrolytic substance to neutralize the charge of the ion-exchange membrane present on the substantial surface, preferably should be such that the electric charge of the electrolytic substance is excessive. Generally, the-larger the amount of the electrolytic substance, the more difficult it is for the organic matter to contaminate the ion-exchange membrane. But if the electrolytic substance is present in too large an amount, it may induce undesirable hydrolysis of water which is quite irrelevant to the objects of the present invention. Therefore, the use of too much electrolytic substance should be avoided. Generally, the amount of the electrolytic substance to be present on the substantial surface should be within the range of 2 X 10' m.eq./dm to 0.5 m.eq./dm based on the amount of the dissociable groups contained therein, preferably within the range of 2.5 X 10 m.eq./dm to 5.0 X l0. m.eq./dm-. The presence of the electrolytic substance of such an amount can be accomplished by using more than 0.0001 mgldm preferably more than 0.001 mg/dm and not more than 500 mg/dm of the electrolytic substance.

The production of the ion-exchange membrane used in the invention which has been subjected to a special surface treatment will be described in detail below. As an ion-exchange membrane to be surface-treated with the treating agent used in the invention, not only may a membranous polymeric substance having ionic groups chemically bonded thereto be used, but also membranous polymeric substances in the form in which ion-exchange groups can be readily introduced by post-treatment can be used. Examples of the latter type include membranous polymeric substances having an aromatic ring in which a sulfonic acid or amino group can be easily introduced, or membranous polymeric substances having chemically bonded thereto functional groups readily convertible to ionic groups, such as haloalkyl groups, halosulfone groups, halocarbonyl groups, carboxylic anhydride residues, or alkyloxycarbonyl groups (RO-CO-). in the present specification, the membranous substances in the form in which an ion-exchange group can be readily introduced by post-treatment will sometimes be called merely raw membrane. The introduction of an ionexchange group into the raw membrane by posttreatment may be performed before or after an electrolytic substance having an opposite electric charge is intimately held on the substantial surface of the raw membrane using the treating agent.

When electrodialysis is performed using the ionexchange membrane used in the invention, various troubles encountered in the conventional electrodialysis for removal of electrolytes hardly occur, and the electrolytes can be removed from the aqueous solution with good efficiency. While no detailed mechanism of this process has yet been elucidated, it is assumed that the following are the reasons for the very good efficiency of the process of the present invention. When an ion-exchange membrane not surface-treated is used for removal of salts by electrodialysis, very small amounts of detrimental ionic organic substances contained in water containing the salts to be electrodialyzed (to be referred to as raw water), such as cationic or anionic surface active agents or ionic substances having a molecular weight of to 300, first adhere to the surface of the ion-exchange membrane. The organic matter permeates through the pores of the ion-exchange membrane, and then is bonded electrostatically'with the exchange groups of the ion-exchange membrane. Therefore, the organic matter blocks the pores of the ionexchange membrane, and in some cases, forms a layer having an opposite charge to the ion-exchange group present on the surface of the ion-exchange membrane to which the organic matter has adhered. This in turn causes an increase in electric resistance, a decrease in current efficiency, and hydrolysis of water in an interface layer between the anionic exchange membrane portion and the cationic exchange membrane portion, and also the neutrality disturbing phenomenon. In contrast, the surface of the ion-exchange membrane used in the present invention has a neutral charge or an opposite charge to the electric charge of the inside of the ion-exchange membrane. Therefore, organic ions such as detergents which are pulled towards the surface of the membrane by electrophoresis are prevented from forming an electrical bond on the surface of the memhydroxyethyl-l-carboxyethyLZ-undecyl brane, and therefore, this prevents the organic ions from depositing on the surface of the membrane or permeating into the interior of the membrane. Consequently, the occurrence of the undesirable phenomena mentioned above can be avoided. The foregoing assumption, it is believed, will also be supported by FIGS. 1 and 2 of the accompanying drawings which show the experimental results obtained in Referential Example and Example 1.

As the ion exchange group having an opposite charge for electrically neutralizing the ion exchange group on the substantial surface of the ion exchange membrane, there are exemplified, in the case of an anionic exchange membrane, a sulfonic acid group, a sulfate group, a carboxyl group, a phosphoric acid group, a phenolic hydroxyl group, a boric acid group, an arsenic acid group, complex salts of transition metals having a negative electric charge, or groups of salts of these. Specific examples of the substance having such an ion exchange group include polystyrenesulfonic acid,

polyvinylsulfonic acid, and salts of these; sulfuric ester of polyvinyl alcohol, and salts thereof; polyacrylic' acid, polymethacrylic acid, and salts of these; copolymers of acrylic or methacrylic esters with at least one vinyl monomer capable of having a negative charge such as maleic acid, itaconic acid, styrenesulfonic acid, or vi nylsulfonic acid; a condensation product of naphthalenesulfonic acid and formalin; ligninsulfonic acid; alkylphosphoric acids and their salts; cellulose derivatives such as carboxy methylcellulose'and its salts; complex salts having a negative electric charge, which contain an alkaline earth metal such as Mg and Ca and a transition metal such as Co, Ni and Fe as acentral metal, and ammonia, ethylene diamine, triethylene tetramine, tetraethylene pentamine, amino acids, etc., as a ligand; and sodium polyphosphate, all having a molecular weight of at least 400. v

in the case of a cationic exchange membrane, compounds having in the molecule a primary, secondary or tertiary amino group,;a quaternary ammonium salt, a stibonium base, or an arsonium base, and complex salts of transition metals having a positive electric charge can be exemplified. Specific examples of compounds having such dissociable groups include polyvinyl pyridines and their quaternary salts; polyvinyl imidazoles and their quaternary salts; polyethylenepolyamines and their derivatives; polyaminostyrene, poly(N- alkylaminostyrene), Poly-N-dialkylaminostyrenes, and poly-N-trialkylammonium-styrene salts; polyvinyl trialkylbenzyl ammonium salts; polyvinylamine, polyallylamine; and complex salts having a positive electric charge, which contain an alkaline earth metal such as Mg or Ca and a transition metal such as Co, Ni, or Fe as a central metal and ammonia, ethylene diamine, triethylene tetramine, tetraethylene pentamine, amino acids, etc. as a ligand, all having a molecular weight of at least 400. In addition to the foregoing, amphoteric electrolytic substances with a molecular weight of at least 400 such as alkylaminoethyleneglycines, 1-

imidozoline, or adenosine-triphosphate may also be cited as being applicable both to the cationic and anionic exchange membranes.

The-ion exchange membrane to be used in the present invention can be produced by the following methods (i), (-ii), and (iii).

6 The first of these methods (i) comprises applying to at least one surface of a known ion exchange membrane a substance having a molecular weight of at least 400. Preferably at least 1,000 and a dissociable group having an opposite charge to the charge of the ion exchange membrane to electrically neutralize the ion exchange group on at least one surface of the ion exchange membrane, or causing an excess of an opposite electric charge of the electrolytic substance applied to be present on at least one surface of the ion exchange membrane. The application of the electrolytic material to the surface of the ion exchange membrane can be performed by any desired means such as immersion of the exchange membrane in a solution, preferably an aqueous solution, of the treating agentpcoating the treating agent on the surface of the ion exchange membrane, 0r spraying it onto the surface. Or a method can be employed which comprises continuously or intermittently feeding an aqueous solution of the treating agent to a solution from which salts are to be removed, using an electrodialysis apparatus using an ionexchange membrane, passing an electric current, and applying the treating agent on the substantial surface of the ion-exchange membrane by electrophoresis.

Specific examples of the treating agent which can be used according to the above mentioned method include polystyrenesulfonic acid, polyvinylsulfonic acid and saltsof these; sulfuric or phosphoric esters of polyvinyl alcohol, and'salts of these; polymers of unsaturated caroxylic acids such as acrylicacid, methacrylic acid, maleic acid, or itaconic acid, copolymers of at least one monomer having a negative charge such as styrenesulfonic acid, vinylsulfonic acid or above-mentioned unsaturated carboxylic acids, with a copolymerizable monomer such as styrene, vinyl toluene, acrylonitrile, methyl acrylate, methyl methacrylate, vinyl chloride, vinyl acetate, vinylidene chloride, acenaphthylene, vinyl ketone, butadiene, or chloroprene; sodium tripolyphosphate; a condensation product of phenolsulfonic acid and formalin; condensation products of benzaldehyde-2,4-disulfonic acid, naphtholsulfonic acid, sodium salicylate, or sodium phenoxyacetate and aldehydes such as formalin, paraformaldehyde, glyoxal, or furfural; high molecular weight ligninsulfonic acid and its salts; a condensation product of naphthalenesulfonic acid and formalin;alginic acid; gum arabic; polyuronic acid; and carboxymethylcellulose, all of which are applicable to the anionic exchange membrane.

Applicable to the cationic exchange membrane are, for example, polyalkylamines; polyvinylpyridienes and their quaternary salts; polyvinylimidazoles and their quaternary salts; polyethylenepolyamines and their derivatives; polyaminostyrenes, poly-N alkylaminostyrenes, poly-N-dialkylaminostyrenes; and poly-N-trialkylammonium styrene salts; polyvinyltrialkylbenzylammonium salts; other soluble polymers having a primary, secondary or tertiary amine or a quaternary ammonium salt such as polyallylamine or polyvinylamine;

as poly(vinyl phosphonium), poly(acrylic phospho-- nium), poly(vinylbenzyl phosphonium),

ROQ/ @011 (wherein R is alkyl), or poly(condensation phosphonium), which are soluble cationic natural or synthetic high polymers.

Also alkylaminoethyl glycin, adenosine triphosphate, proteins such as gelatin or casein, and l-hydroxyethyll-carboxyalkyl-Z-alkylimidazolines which are treating agents applicable-both to the cation exchange membrane and anion exchange membrane can be used.

The methods (ii) and (iii) to be described are based on the covalent bonding of the treating agent and the ion-exchange membrane.

Method (ii) involves causing the treating agent to be adsorbed on the surface of the ion-exchange membrane, and then graft-copolymerizing them with each other by a radical-generating means suchas light, X- ray, radioactive ray, or corona discharge. As previously mentioned, in the case of using methods (ii) and (iii),.

it is not necessary for the treating agent itself to have a molecular weight of at least 400. Therefore, in addition to those'exemplified with respect to method (i) above, for cation exchange membranes, vinyl imidazoles, vinyl anilines, vinyl N-trialkylbenzyl ammonium salts, vinyl N-dialkylbenzylamines, or vinyl N-monoalkylbenzylamines may also be used as the treating agents, and these may be graft-copolymerized with styrene, vinyl chloride, vinyl acetate, acrylonitrile, methyl acrylate, methyl 'methacrylate, vinylidene chloride, acenaphthyene, vinyl ketone, divinyl benzene, divinylsulfone, butadiene, or chloroprene. For anion exchange membranes, vinyl monomers which are anionic or capable ofbeing anionic upon post-treatment, such as styrenesulfonic acid, vinylsulfonic acid, allylsulfonic acid, acrylic acid, methacrylic acid, maleic acid, itaconic acid, or salts or esters of these may be polymerized or copolymerized similar to the case of the cation exchange membranes. The graft-copolymerization may be effected advantageously by using photosensitizers or radical initiators at the same time.

Method (iii) can be performed by any of the following procedures (a) to ((1).

Procedure (a) comprises haloalkylating only the substantial surface of a raw membrane or a polymeric membrane, treating the surface with an electrolyte having a primary, secondary or tertiary amine group, and then sulfonating the interior of the membrane in a customary manner to form a cation exchange membrane. Examples of the amino compound that can be used conveniently in this procedure-include aromatic amines such as aniline, phenylene diamines, or phenylene triamines; aliphatic amines such as ammonia, hydrazine, alkylamines, dialkylamines, trialkylamines, ethanolamine, diethanolamine, triethanolamine, ethylenediamine, diethylene triamine, triethylene te'tramine, or tetraethylene pentamine; polymers having a primary, secondary, or tertiary amino group such as polyethylene imine, polyvinvyl pyridines, polyvinyl amine, polyallylamine, or polyvinyl imidazole; and heterocycle compounds having a primary, secondary, or tertiary amino group such as dipyridine, tripyridine, tetrapyridine, pyridine, aminoquinones. Dyes such as Bismarck Brown G. (C! 21000), Janus-Brown R (Cl-33505), Basic Blue Co. (Cl-52025), New Methylene Blue NSCONE (Cl-52030), or Bromocyanine BXCONC can also be used.

Procedure (b) comprises haloalkylating a raw membrane or polymeric membranous substance uniformly to its interior, contacting the surface of the membrane with a compound having at least one-functional group which is capable of becoming a cationic exchange group and at least one primary, secondary, or tertiary amino group to thereby cause the cationic exchange group only on the substantial surface of the membrane, and then aminating the haloalkyl group in the interior of the membrane with ammonia or an amino compound such as alkylamines, dialkylamines, trialkylamines, monoethanolamine, diethanolamine, triethanolamine, or dimethyl monoethanolamine to form an anion exchange membrane. Examples of the compounds having both an amino group and a functional group capable of becoming a cationic exchange group include amino acids, iminodiacetic acid, aminophenols, aminocresols, aminocaproic acids, aminotoluenesulfonic acids, anilinesulfonic acids, aminobenzoic acids, aminonaphthalenesulfonic acids, aminonaphtholsulfonic acids (for example, 8-amino-1,3,6-naphthalenetrisulfonic acid, 4-amino-l-naphthalenesulfonic acid, or salts of these), aminosalicylic acids and their salts, and dyes .having a primary, secondary, or tertiary amino group and a functional group capable of becoming an anion such as sulfonic acid or carboxylic acid groups, the examples of the dyes being Diamond Fast Red B (Cl-17075), Mitsui Anthracene Blue SWGG (Cl-58805 Fast Acid Green SS (Cl-20440), Chrome Fast Green S (Cl-26925), or Yamada Chrome Brown GL.

Procedure (c) comprises introducing into the substantial surface the raw membrane at least one of sulfonyl halide, carboxylic acid halide, phosphonyl halide, phosphorus halide (PXn) (wherein n is 2 or 4 and X is halogen), or carboxylic anhydride group (these groups will be referred to generically as acid halide group), treating it with a primary, secondary, or tertiary amino compound to form an acid amide bond or a P-N bond, and thereafter introducing a cationic exchange group into the interior of the membrane by a chemical reaction such as sulfonation or converting it to a cationic exchange group by such means as hydrolysis. An alternative process comprises preparing a raw membrane having the above-mentioned acid halide group only on the substantial surface thereof. hydrolyzing it or contacting it with a compound having at least one functional group capable of becoming a cationic exchange group andat least one primary or secondary amino group as mentioned above with respect to (b) to thereby cause the cationic exchange group to be present only on the substantial surface of the membrane, and thereafter introducing an anionic exchange group into the interior of the membrane by the conventional method such as chloromethylation followed by amination or converting it to an anionic exchange group, to thereby form an anionic exchange membrane to be used in the present invention. Specific examples of the amino compound that is suited for use according to this procedure include ethylene diamine, diethylene triamine, triethylene tetramine, tetraethylene diamine, tetraethylene pentamine, 2-aminopyiridine, 3- aminopyridine, 4-aminopyridine, piperazine, ethanolamine, diethanolamine, p-aminosalicylic acid, maminosalicylic acid, known amino acids, aminopterine, aminoquinolines, aminophenols, aminomethylphenols, aminomethylthiazoles, aminobenioic acids, amidol, aminoacetophenone, aminobenzophenone, vitamins having a primary or secondary amino group, iminodiacetic acid, 2,4-dinitrophenyl hydrazine; phenylene diamine, dicyandiamide, phthalimide, phenylglycine, Bismarck Brown (Cl-21000), Auramine conc (CI- 41000), Magenta (Cl-42510), Chrysoidine Crystal (C.I-l 1270), polyethyleneimine, polyvinylamine, polyallylamine, and polyaminostyrene.

Procedure (d) involves treating only the surface of a raw membrane whose interior contains uniformly at least one of the acid halides mentioned 'with respect to procedure above, with a primary or secondary amine to cause an anionic exchange group to be present on the surface of the membrane, and thereafter hydrolyzing the acid halide group present inside the membrane and introducing a cationic exchange group into the interior of the membrane, to thereby form a cation exchange membrane. The amines suitable forum in this procedure are the same as those exemplified with respect to procedure (c). In an alternative procedure, the acid halide group. alone on the substantial surface of the membrane is hydrolyzed to cause a cationic exchange group to be present, and on the other hand, the acid halide group present inside the membrane is treated with a polyamine such as diamines or triamines to introduce an anionic exchange group into the interior of themembr ane and to form an anion exchange membrane.

In the present invention, any known electrodialysis method and apparatus can be used. In actual operation according to the process of the invention, pure water is produced by electrodialysis at room temperature to 90C. using an apparatus wherein a plurality of cation exchange membranes and anion exchange membranes are aligned alternately to form passes of a feed solution and passes of a concentrated solution alternately. The,

ion exchange membranes should be so disposed that their surfaces subjected to the specific surface treatment of the present invention at least come into contact with the feed solution.

Xbr'difigib'afimher aspect of the present invention, a process is provided for removing electrolytes from water, which comprises disposing cation exchange 1'0 membranes and anion exchange membranes alternately in an aqueous solution containing electrolytes to thereby form a plurality of chambers containing the ion exchange membranes as partition walls, and passing a direct current in series through the chambers to thereby pass cations and anions present in the aqueous solution through the cation exchange membranes and anion exchange membranes respectively and therefore reduce the concentrations of the electrolytes in the aqueous solution, each of the exchange membranes consisting of an insoluble, infusible synthetic organic polymer having dissociable ionic groups chemically bonded thereto and having pores through which ions pass the membrane, at least one substantial surface of the ion-exchange membrane intimately retaining an electrolytic substance having an opposite electric charge to the charge of the ion-exchange group of said ion-exchange membrane and being incapable-of pass- 59591592sh5h939r92f t aisn-s shsass. mem r ne Some of the ion-exchange membranes that are used in the present invention have already been known to be useful for concentrating sea water, but none-of them has ever been used for removing salts from water. It is surprising that according to the process of the present invention, an electric resistance does not increase remarkably, the current efficiency is not reduced during the electrodialysis procedure, and also the neutrality disturbing phenomenon hardly occurs.

The following Examples and Comparative Examples will illustrate the present invention, and are not intended in any way to limit the scope of the invention. ""The ion-exchange membranes used in these Examples and Comparative Examples were pre-treated. In

the case of those used after adsorbing electrolytic substances thereto, cation exchange membranes were immersed alternately in 1.0N HCI and 0.5N NaCl to equilibrate their properties fully, and then equilibrated with a measuring solution not containing organic ions; anion exchange membranes were immersed alternately in 1.0N HCI and 0.5NNH OI-I to equilibrate its properties fully, and then equilibrated with the above solution. In the case of those having the electrolyte chemically bonded thereto by a covalent bond, cationic exchange membranes were treated with LON HCI and 0.5N NaCl to equilibrate its properties; anionic exchange membranes vwe're treated with 1.0N HCI and 0.5N NH OH to equilibrate its properties.

The two chamber type cell used. was a cell made of acrylic resin consisting of two chambers each having an inner volume of 120 cc and having an ion-exchange membrane with an ion-exchange area of 5 X 2 cm. Within the cell silver-silver chloride electrodes were provided for passing an electric current and probesilver-silver chloride electrodes spaced from each ionexchange membrane surface by a distance of 2 mm for measuring voltage. The probe-electrodes were connected to an X-t recorder to measure the changes with time of the electric resistance of the membrane during the electrodialysis. At the same time, after passing an electric current for a predetermined period of time, the pH and current efficiency of the solution were also measured. The current efficiency was'determined by the following equation using a copper coulometer.

esteem;

Equivalents of ions transported through the membrane X Weight increase of copper plate The electrical resistance of the membrane was measured in 0.5N NaCl aqueous solution at 25C. at alternating current of 1000 cycles.

REFERENTIAL EXAMPLE A pasty mixture composed of 100 parts of finely divided polyvinyl chloride, 160 parts of 2-methyl-5- vinylpyridine, parts of styrene, 10 parts of 50 percent pure divinylbenzene, 25 parts of dioctyl phthalate, and a part of benzoyl peroxide, was daubed onto polyvinyl chloride cloth. The daubed mixture was polymerized in situ under heating at 90C. for 5 hours, while both surfaces of the cloth were covered with cellophane. The resulting filmy product was treated with a solution composed of 50 parts of methanol and 50 parts of methyl iodide, at 25C., for 20 hours. Thus an anionexchange membrane containing a quaternary ammov nium salt as the exchange group was obtained, which had an electrical resistance of 3.5Q-cm and a current Table 1 Current pH of the Solution in the Cell Aqueous Solution M 7 7 Anode chamber Cathode chamber EXAMPLE 1 The same anion-exchange membrane employed in the above Referential Example was immersed in the electrolyte specified in Table 2 for the time also specified in the same table, and thereafter the electrodialysis was performed similarly to the Referential Example. The anode chamber of the cell was filled with 0.05 N- NaCl solution, and the cathode chamber was filled with efficiency of.98 percent, as determined by electrodial- 0.05 N-NaCl solution containing 100 ppm of sodium ysis in two-chamber type cell filled with 0.5 N-NaCl aqueous solution.

dodecylbenzenesulfonate. The voltage variations in the R aNQ w a s awl G- Table 2 Electrolytic Solution Results Treating Average Concentra- Time Adsorbed Current Anode Cathode Run Electrolyte Molecular tion (hrs.) Quantity Efficiency Chamber Chamber No. Weight (ppm) (meqldm (17) (pH of Solutions) l Formalin condensate I of sodium naphtha- 2,400 10,000 16 0.03 98 6.1 5.9

lenesult'onate 2 ditto 2,400 W0 16 0.012 98 6.1 5.8 3 Sodium polystyrenesulfonate 15,000 10,000 l6 0.03 95 6.8 5.3 4 Sodium polyacrylate 10,000 10,000 24 0.01 92 7.1 5.1 5 Sodium polyvinylsulfonate 50,000 3,000 16 0.009 95 6.8 5.3 6 Sodium ligninsulfonate 5,000 10,000 l6 0.007 96 6.4 5.6

The anion-exchange membrane was inserted in a EXAMPLE 2 two-chamber type cell, and electricity was passed through the below-specified aqueous solution therein,

at a current density of 0.25 A/dm for 3 hours to effect electrodialysis. In the meantime, the current efficiency, pH of the solution in two chambers'after the electrical charging, and voltage variation during the run, were measured, with the results as shown in Table l, and the graphs Nos. 1 and 2 of FIG. 1.

The aqueous solution: No. l: 0.05 N-NaCl solution in both anode and cathode chambers No. 2: 0.05 N-NaCl solution in anode chamber, and

0.05 N-NaCl solution containing 100 ppm of sodium dodecylbenzene-sulfonate in cathode chamher. No. 3: The cell was electrically charged for 3 hours to effect electrodialysis under the conditions of No. 2 above. Then the aqueous solution in the cell was once discarded, and refilled with the solutions of No. 2. The electrodyalysis was repeated once again (not shown in FIG. 1).

A pasty mixture composed of 35 parts of finely divided polyvinyl "chloride, parts of styrene, 10 parts of 50 percent pure divinylbenzene, 25 parts of dioctyl phthalate, and 2 parts of benzoyl peroxide, was daubed onto polyvinyl chloride cloth, and allowed to polymerize in situ at C. for 4 hours, while both surfaces of the cloth were covered with cellophane. The filmy product obtained was immersed in a chloromethylating bath composed of 80 parts of carbon tetrachloride, 20 parts of chloromethyl ether, and 3 parts of anhydrous tin tetrachloride, at 25C., for 5 hours, to be chloro methylated. The chloromethylation reaction was terminated by immersing the membrane in methanol. Thereafter the product was immersed in a saturated aqueous solution of sodium l-amino-8-naphthol-3 ,6- disulfonate, for 2 hours, to be reacted at its surface portions only. The inner portion of the filmy product was treated by immersing the same in 30 percent trimethylamine aqueous solution for 8 hours. Thus, a strongly basic anion-exchange membrane having a quaternary 13 a rnrnoniiir n salt as the ion-exchange group was 55 tained.

The membrane was used in electrodialysis under the conditions identical with those of Referential Example, with the results as shown in Table 3 below. The given probe-electrode voltages are the highest values reached during the whole run (approximately 4.5 hours after the electrical charging started).

TABLE 3 EXAMPLE 4 Results Run Aqueous Solution ProbepH of Solution No. to be Treated Efficiency electrode (51) voltage Anode Cathode (volts) Chamber Chamber 1 pas concentration: s9 0 3.2 1.9 4.5 y

P im 91" 2 Fikfiitts 9a 0.2 15.1 5.9

3 D85 concentration; 95 1.2 6.5 5.7'

00 p 4 7N0 nas 96 0.2 6.2 5.9

Aniang'tnaassmzun amnesia arise a r E CBH trols, in which the membranes preparedas in Example 2 except that the surface treatment of this invention was omitted, were used. In Table 3, DBS standsfor sodium dodecylbenzenesulfonate. i

EXAMPLE 3 The filmy product obtainedin Example 2 was treated in 60C., 98 percent conc. sulfuricacid for l2hours.} The cation-exchange. membrane (untreated) obtained? was setin a two-chamber type cell. The cell was filled with 0.05 N-NaCl solution containing 100 ppm of dodecy lpyridinium chloride as the anolyte, and 0.05 N- NaCl solution, as. the catholyte, and. the electrodialysis was effected at the current density of 2.5 mA/cm. The

alysis similar to theabove. An amount of polyethylene-' imine adsorbed on the surface of the membrane was 0 s 1 T he qbsrs s flaw ess. sssrds the maximum level of 0.56 volt at approximately 4 TABLE 4' A pasty mixture composed of parts of methyl acrylate, 10 parts of 50 percent pure divinylben'zene, 25 parts of dioctyl phthalate, 2 parts of benzoyl peroxide, and parts of finely divided polyvinyl chloride, was daubed onto a cloth made of glass fibers, and polymerized in situ at C. for 4 hours, while both surfaces of thecloth were covered with cellophane. The filmy product obtained was hydrolyzed with an alcohol solution of 8 percent caustic potash, to be converted to a weakly basic cation-exchange membrane.

Separately, the above cation-exchange membrane was immersed in quaternarized product (molecular weight: 10,000.) of poly-2-methyl-5vinylpyridine (quater-,

narized with methyl iodide; concentration, 1,000 ppm) for 24 hours. An amount of the substance adsorbed on the surface of the membrane was 0.005 meq/dm The above weekly basic cation-exchange membrane and that which was surface-treated'in accordance with the invention were each used in electrodialysis performed in two-chamber type cell at a current density of 2.5 mA/cm The respective voltage variation during the run, as well as the current efficiency and pH of the solution after 24 hours electrodialysis were as given in Table 4 below. The anolyte in the cell was a liquid mix- .ture .of 0.025 N-NaCl and 0.025 N-CaCl Referring to Table 4, Run Nos. 2 and 4 were performed with the anolyte of above-specified composition plus cetyltrimethylamrnonium chloride which was added .to a concen- .tration of 50 ppm.

pH of Treated Voltage (mV) Variation H Liquids Ciir' rent Run lon- Effici N0. Exchange ,0 10 30 l 4 24 ency Anode Cathode Membrane (min.) (min.) (min.) (hr.) (hm) (hrs) Chamber Chamber .troltod 250 250 250 250 250 250 98 6.l 5.9 membrane 2 ditto 250 .520 770 1080 i500 1300 88 8.5 3.8 3 Treated mi membrane 330 10L 260 250 250 98 6.2 6 .0 4 ditto 300 260 250 260 280 260 97 6.5 5.7

I Ratio of Percent 1011 11W EXAMPLE l. A polymer latex from 30 parts of styrene and 70 parts of butadiene was daubed onto glass fabric and dried. The filmy product obtained was subjected to 5 cross-linking reaction at 20C. for 48 hours, in a cyclizing reaction bath composed of 100 parts of ethylether and 250 parts of titanium tetrachloride. Then the product was immersed in a chloromethylating bath composed of 100 parts of chloromethyl ether, 67 parts of ethylene dichloride, and 19 parts of anhydrous aluminum chloride, at 20C. for 5 hours. Thus chloromethylated product was further aminated in a 30 percent trimethylamine aqueous solution at 30C. for 5 hours.

Thus an anion-exchange membrane was obtained. The 15 flow velocity of 10 cmsecf, and the cell voltage was set at 22.5 volts. The electrodialysis could be effected at the initial current density of 0.3 A/dm The electrodialysis was subsequently continued for days at constant voltage. The current densityvariation in the meantime was as shown in Table 5, No. l. 30

Separately, the electrodialysis of the above liquid mixture was performed, while -a formalin condensate (molecular weight: 2,400) of sodium na'phthalenesulfonate was added to the liquid mixture at a rate of 2 ppm per hour per day for the first two weeks, and thereafter at a ratio of 0.1 ppm per hour per day. The results were as shown in Table 5, No. 2. In this case, it was confirmed by adsorption test that, on the substantially surface portion of the anion-exchange membrane, at least 0.008 meq/dm of the condensate was present.

TABLE 5 Current Density (A/dm) Variation 11th 2t 1 Density Day Day Day Day Day No. l 0.30 0.29 502a 0.27 0.25 0.20 I No. 2 0.30 0.30 0.30 0.29 0.29 0.22

The current efficiency after the 30' days continuous running was 82 percent in Run No. 1, and 92 percent in Run No. 2. Those results demonstrate that the ratio of ion removal was reduced in Run No. l to 0.637,

EXAMPLE 6 The filmy product obtained in Example 2 was immersed in a chlorosulfonic acid solution consisting of 1 part of carbon tetrachloride and 2 parts of at least 90 percent pure chlorosulfonic acid, at 10C. for 2 hours. Thus chlorosulfonic acid groups were uniformly introduced throughout the inside of the filmy product. The product was then immersed in a 5 percent aqueous solution of polyethyleneimine (molecular weight: 30,00- 0) for 16 hours, to fix the polyethyleneimine on the surface of the membrane through an acid amide bond. The product was then further immersed in lN-NaOH aqueous solution to convert the unreacted chlorosulfonic acid groups present in the product to sulfonic acid ;groups. Thus a cation-exchange membrane with polyethyleneimine fixed on its surfaces was obtained.

The membrane was set in a two-chamber type cell, and electrodialysis was effected therein at a current density of 25 mA/cm using as the anolyte 0.05 N- NaCl aqueous solution containing 200 ppm of acetate of dodecylamine, and as the catholyte, 0.05 N-NaCl aqueous solution. The probe-electrode voltage of the cation-exchange membrane was 0.32 volt when the :electrical charging started, which rose to the maximum level of 0.59 volt after 4.5 hours running, and thereafter gradually fell. In contrast, when the cationexchange membrane which was not surface-treated was used in the electrodialysis under identical conditions, the probe-electrode voltage was initially 0.31 volt, which rose to 2.15 volts after 30 minutes.

EXAMPLE 7 To a mixture of parts of butyl ester styrenesulfonate acid, 20 parts of styrene, and 10 parts of 5 0 percent pure divinyl benzene, 60 parts of dioctyl phthalate and 2 parts of benzoyl peroxide were added, and the resulting mixture was poured into -0.5-mm wide space between two sheets of glass, to be subsequently polymerized at C. for 5 hours. Then the glass sheets were removed, and as sheet'of filmy product was obtained. The product was heated at 60C. for 12 hours in 8 percent methanol solution of caustic potash, to hydrolyze the ;ester linkage, and then thoroughly washed with lN-HCl and 0.5N-NaCl. Thus a cation-exchange membrane was immersed in a mixed liquid composed of 2 parts of polyethyleneimine (molecular weight: 5,000), a part of benzophenone and 97 parts of methanol, for 30 minutes. Then one surface of the membrane was covered with quartz plate, and irradiated for an hour with ultraviolet rays from an ultraviolet ray lamp, model SHLS- 1002 B manufactured by Toshiba Co., Japan at a distance of 5 cm. The membrane was thoroughly washed first with methanol, and then again with lN-l-lCl and 5 0.5N-NaCl. The grafted quantity of polyethyleneimine was 0.06 meq/cm This membrane was set in a two-chamber type cell with its photo-irradiated side facing the anode, and electrodialysis was effected for 12 hours at the current compared with Run No. 2. Incidentally, the ratio of ion 60 d i f 30 m A/cmz, using ()5N C C1 as the cathoremoval was calculated in accordance with the equation below: i

Current density after 30th day in No. 1

Current density after 30th day in No. 2

X 30th day in N0. 1

Current efficiency after X 30th day in N0. 2

Current efliciency after 65 lyte, and 0.05N-CaCl containing ppm of cetyltrimethylammonium chloride as the anolyte. Thus measured voltage variation, current efficiency, and pH of the solutions in two chambers after 12 hours running, were as given in Table 6 below. As a control, the same experiment was repeated with the membrane not subjected to the above electrolytefixing treatment. The results are also given in Table 6, as Run No. 2.

18 Table 6 Type of Voltage (rnV) Vlrin'tlon Current pH of Treated Run Ion Effici- Liquids No. Exchange 1 ency Membrane 30 2 r 8 I2 (52) Anode Cathode (min.) (min.) (hrs.) (hm) (hrs.) Chamber Chamber 1 Treated membrane 670 750 780 820 890 95 6.2 6.0 2 Untreated membrane 620 1050 i550 1950 1620 87 8.5 3.9

EXAMPLE 8 o le'ate was added to the NaCl solution in the cathode A pasty mixture composedof 180 parts of styrene,

' parts of SO'percent pure divinyl benzene, parts of chamber only, to a concentration of 100 ppm (Run Nos. 2 and 4), and the cells were electrically charged. The results were as shown in Table 7 below.

parts of finely divided polyvinyl chloride, was daubed onto polyethylene net. Then bothsurfaces of the net were coveredwith cellophane, and the mixture daubed thereon was polymerized in situ at 110C. for 4 hours.

methacrylic acid, 78 parts of methanol and 2 parts of benzophenone was-uniformly sprayed onto one surface of the anion-exchange membrane prepared as above,

and the surface was covered with a quartz plate to prei vent evaporation of the liquid mixture, while it was irradiated from an ultraviolet ray lamp, model SHL-l00 uv (product of Toshiba Co., Japan) placed 5 cm apart from the surface, for 30 minutes. Then the photoirradiated membrane was thoroughly washed with 0.lN-NaOH aqueous solution, remove the homopolymer of acrylic acid and unreacted acrylic acid. Thus an anion-exchange membrane treated in accordance with this invention was obtained. On the surface of such anion-exchange membrane, a grafted polymer of 67 in average degree of polymerization was present, and the cation-exchange group introduced by the grafting was 007 meqldm The untreated and treated membranes were separately'set in two similar two-chamber type cells, the photo-irradiated surface of the treated membrane facing the cathode. As to each of the cells, the probe-i electrode voltage variation and current efficiency after 24 hours running were measured, when 0.04 NaCl solu- 1 tion was poured into the two chamber parted by the i membrane (Run Nos. 1 and 3 of Table 7) andsodium (untreated).

TABLE 7 Type of Voltage (mV)' Variation Current Run lon- Effici- N 0. Exchange 0 10 30 l 4 18 24 ency Membrane (min.) (min.) (min.) (hr.) (hrs.) (hrs) (hrs.) ('5) 1 Untreated membrane 280 280 280 280 280 280 280 9B 2 ditto 280 290 300 315 360 410 400 89 3 Treated membrane 295 290 290 290 290 290 290 97 4 ditto 295 290 290 290 300 310 315 96 dioctyl phthalate, 2 parts of benzoyl peroxide, and 100 EXAMPLE 9 lymerized in situ. The filmy product obtained was immersed in benzoylating bath composed of 500 parts of carbon tetrachloride, 40 parts of anhydrous aluminium chloride and 34 parts of benzoyl chloride, at room temperature for 4 hours, so as to be benzoylated. Then the product was washed with methanol, dried, and sulfonated with 60C. 98 percent conc. sulfuric acid for 8 hours, to be converted to a cation-exchange membran Separately, this H-type catiomexchange membrane was further washed with methanol, immersed in 50 percent methanol solution of Z-methyl-S-vinyl-pyridine for 1 minute, and irradiated with an ultraviolet ray lamp Model SHLS-l002B of Toshiba Co., Japan, placed 5 cm apart from the membrane surface which was covered with a quartz plate, for l0 minutes. Thus a cationexchange membrane on which the specified electrolyte was fixed was obtained. On the irradiated surface, 0.03 meq./dm of poly(2-methyl-5-vinylpyridine) was present,

Then the membrane was immersied alternately in lN-HCl solution and 0.5N-NaCl solution until it became sufficiently equilibrated. Thereafter the membrane was set in a two-chamber type cell the cathode chamber of which was filled with 0.05N-NaCl and the anode chamber, with 0.05N-NaCl containing ppm of tetradecylpyridinium chloride. The treated membrane was set with its photo-irradiated surface facing the anode chamber. Thus the electrodialysis was effected at a current density of 2.5 mAlcm The voltage variation during the electrical charging, and current efficiency and pH of the solutions in the anode and cathode chambers after 24 hours running were as shown in Table 8 below.

cial neutral detergent (composed chiefly of sodium dodecylbenzenesulfonate) as the catholyte, and 0.05N- NaCl solution as the anolyte. The performance of the membrane measured similarly to Example 9 was as shown in Table 9, in which Run No. 1 is a control using the untreated membrane.

The same filmy product obtained in Example 1 was chloromethylated in a chloromethylating bath composed of 100 parts of carbon tetrachloride, 20 parts of washed with methanol, and then immersed in percent trimethylamine aqueous solution for 5 hours, to form a strongly basic anion-exchange membrane (untreated).

TABLE 8 Type of Voltage (mV) Variation Current pH of Treated Run lon- Effici- Liquids No. Exchange 0. 30 2 8 24 ency Anode Cathode Membrane (min.) (min.) (hrs.) (hrs.) (hrs.) (5) Chamber Chamber 1 Untreated membrane 350 600 850 1020 1250 92 8.8 3.6

. 2 Treated membrane 490 $00 515 580 650 98 6.5 6.1

TABLE 9 Type of Voltage (mV) Variation Current pH of Treated Run lon- Effici Liquids No Exchange 0 30 I 2 i6 24 ency Anode Cathode Membrane (min.) (min.) (hrs.) (hrs.) (hrs.) (11) Chamber Chamber 1 Untreated membrane 295 320 340 390 420 91 7.5 4.9

2 Treated membrane 315 315 320 330 345 97 6.4 6.1

EXAMPLE 10 M T M EYWTLE TI Y M M Commercial polyethyleneimine (molecular weight: 100,000) was dried by freeze-drying, and converted to anhydrous polyethyleneimine. 43 parts of the anhychloromethyl ether, and 3 parts of tin tetrachloride, drous polyethyleneimine were dissolved in 100 parts of This anion-exchange membrane was immersed alter- 45 lamp, Model SHLS-l002B of ToshibaCo Japan,

placed 5 cm apart from the covered surface. The membrane was thoroughly washed with water, and again alternately immersed in 0.5N-NaCl and LON-HCI solutions to be given an equilibrium property. Thus an electrolyte-fixed anion-exchange membrane (treated) was obtained, one surface of which held 0.09 meq/dm of polystyrenesulfonic acid. This ion-exchange membrane was set in a two-chamber type cell with its photoirradiated surface facing the cathode. Electrodialysis was effected in the manner similar to Example 9. using 0.05N-NaCl solution containing 200 ppm of commer-' methanol, 28 parts of epichlorohydrin were added and parts of methanol were further added. The resulting mixture was poured onto a glass sheet covered with a glass fabric, and dried for 2 hours at C. to form an anion-exchange membrane (untreated), which was sufficiently immersed in lN-l-lCl and 0.5N-NH OH alternately, to be given an equilibrium property. Thereafter the membrane was further immersed in 0.05N-NaC1 solution.

Separately, the anion-exchange membrane, identical with the above wasimmersed in a liquid mixture of 1 part of benzoyl peroxide, 5 parts of methacrylic acid, and 94 parts of methanol, for one minute, and then irradiated for 20 minutes with the ultraviolet ray lamp similarly to Example 9. Thus an anion-exchange membrane on which the specified electrolyte was fixed was obtained (treated membrane), one surface of which retained 0.03 meqldm of methacrylic acid as graftpolymerized. The membrane was thoroughly washed with methanol, and then given .the equilibrium property through the treatments similar to those given to the untreated membrane.

The untreated membrane and treated membrane were separately set in two similar two-chamber type cells, in which electrodialysis was performed similarly to Example 9. 0.05 N-NaCl was used as the anolyte, and 0.05N-NaCl aqueous solution containing 200 ppm of C'smmetaar'nettai"aete ett "'(ehireaiitponefiiz s6 dium dodecylbenzene-sulfonate), as the catholyte. The performance of the membranes was measured similarly to Example 9, with the results asv given in Table 10 below.

EH65 containing 300 ppm of commercial in vert soap (dodecyltrimethylammonium chloride), and as the catholyte, 0.08N-NaCl aqueous solution. The data obtained through the experiment were as shown in Table 11 below.

TABLE 10 Type of Voltage (mV) Variation Current pH of Treated Run Ion- Effici- Liquids No. Exchange 30 2 8 24 ency Anode Cathode Membrane (min.) (min.) (hrs.) (hrs.) (hrs.) Cham bet Chamber 1 Untreated 7 membrane 290 '310 320 340 380 83 7.1 5.5 2 Treated i membrane 300 300 305 310 318 88 6.3 6.0

TABLE 11 Quantity of r v Cation- Voltage (rnV) Variation pl-lof Treated Type of Exchange Current Liquids Run lon- Group Effici- No. Exchange Present on ency Membrane Membrane 0 30 4 24 (5) Anode Cathode Surface (min.) (min.) (hrs.) (hrs. 0 Chamber Chamber 7 (meqfim i' 1 f a l i a W0.- mm

trelted M 250 1350 1100 a 780 82 3.8 8.5 M. membrane 2 Treated membrane 0.09 meq/dm 250 350 410 480 96 6.0 6.2 No. 1

3 Treated 1 membrane 0.02 meq/dm' 260 380 450 520 94 .7 6,4 No. 2

EXAMPLE 12 m'mmmmm "EXAMPLE If;

The untreated cation-exchange membranes as obtained in Example 3 were each daubed with the electrolyte of the below-specified composition, covered airtightly with cellophane, and irradiated for 240 hours. from Co -60 of 3,000 curies as the radiation source, at a distance of CmLThen the membranes were thoroughly washed with water.

Compositions of electrolytes:

1. 1 percent aqueous solution of polyethyleneimine I (molecular weight: 10,000)

2. 1 percent methanol solutionof Cl-type quaternary salt of 'poly-4-vinylpyridine (molecular weight: 150,000)

The treated membranes thus obtained (the polyethyleneimine-fixed membrane being labeled No. l, and the other'No. 2) and the untreated membrane were separately set in three similar two-chamber type cells. In all cells electrodialysis was effected similarly to Ex- Compositions of electrolytes:

1. 1 percent aqueous solution, of polystyrenesulfonic acid (molecular weight: 150,000)

2. 1 percent aqueous solution of condensate (molecular weight: 2,400) of naphthalenesulfonic acid and formalin The ab oiie two membranes were used in electrodialysis similarly to Example 12, using as the anolyte ample 9, using as the anolyte 0.08N-NaCl aqueous s0 5 0.05N-NaCl aqueous solution containing 250 ppm of commercialheutral detergentcomposed chiefly of 5 dium alkyl-benzenesulfonate. The measurements were taken similarly to Example 9, with the results as given in Table 12 below.

Table 13: The treating liqiiids employed in the electrodialysis were: 0.05 N- KCl aqueous solution as the anolyte, and 0.05 N- KCl solution containing 100 ppm of sodium dodecyl benzenesulfonate as the catholyte.

similarly to Example 9, with the results as given in 65 TABLE 12 CurpH of Treated Voltage (mV) Variation rent Liquids Type of Qh;ti;j Run lonof 'Ii'e at- Effi- No. Exchange ing Agent 30 2 4 24 ciency Anode Cathode Membrane (meq/dm') (min.) (min.) (hra.) (hm) (hm) Chamber Chamber treated 210 15,000 13,000 10.000 5.000 76 9.5 3.8 membrane 2 Treated 0.01

membrane meq/dm' 205 800 1,300 1,200 700 90 7.0 5.2

No. 1 3 Treated 0.002

membrane meq/dm' 220 210 230 240 240 98 6.2 6.0

No. 2 MM Table 13 C m g i "m A CurpH of Treated Type of Quantity Voltage (mV) Variation rent Liquids Run lonof Treat- Effl- No. Exchange ing Agent 0 2 4 24 ciency Anode Cathode Membrane (meq/dm') (min.) (min.) (hm) (hrs.) (hm) (11) Chamber Chamber treated 220 12,000 9,500 8,000 4,000 81 9.5 3.9 membrane 2 Treated membrane 0.03 230 280 350 380 500 97 6.5 5.8

No. 1 3 Treated membrane 0.04 220 235 250 280 320 98 6.4 6.0

' 'EX'KMPEEIZ i V EXAMFLE 15 v The anion-exchange membrane (untreated as ob- The electrolytes of below-specified compositions tained in the Referential Examples was fixed on 0.05 were fixed onto the cation-exchange membranes (uncm thick polyethylene film with vinyl adhesive tape, treated) as obtained in Example 3, through the proceand onto which the electrolyte of the below-specified dures similar to those described in Example 14. The composition was caused to be present by the belowcation-exchange membrane obtained treated with the specified treatment. Then the membrane was subjected electrolyte (1) below was labeled treated membrane to the corona discharge effected with a corona dis-. No. 1, and that treated with the electrolyte 2), treated charge equipment (product of Kasuga Electric Co., Jamembrane No. 2. pan, 1 KW type) at a frequency of 110 KHZ 5 KHZ Both membranes were thoroughly washed with waand output voltage of 3KV, with the film feed rate of ter, given equilibrium property through alternate im-' 10 m/min. The anion-exchange membranes treated in mersions in 1.0 N- HC1 and 0.5 N- NaCl, and used in accordance with this invention (that subjected to the the test similarly to Example 14. The results were as treatment (1) below is labeled as treated membrane given in Table 14 below. The treating liquid was 0.05 No. l, and the other, treated membrane No. 2) were N- NaCl, the anolyte only containing 100 ppm of dodeobtained. cylpyridinium chloride.

I. Methacrylic acid: 20 parts The membrane was immersed Benzophenone: 1 part in the mixture for 1 minute I. 2-methy1-5-vinyl- 50 parts daubed uniformly onto the Methanol: 50 Parts pyridine: membrane surface with absorbent 2. Ligninsulfo nic acid: 5 parts The mixture was uniformly M thanol; 50 parts cotton Acrolein: 1 part sprayed onto the membrane 2. 5 parts Methanol: 94 parts surface Polyethyleneimine:

a,a'-Azoiso- 4 The properties of those membranes were measured 'gjggggjjfi l gj 5 m'nuws 'mme'slon hours, thereby providing cation-exchange membranes having sulfonic acid groups. The membrane fixed with the above electrolyte (l) was labeled treated br n .NQ- 1, n that w the 191XEQLEE TABLE 14 1 Type of Quantity \i'oltage (mV) Variation CurpH of Treated [onof Treatrent Liquids Run Exchange ing Effi No. Membrane Agent 0 i 30 2 4 24 ciency Anode Cathode (meq/dm') (min.) (min.) (hm) (hm) (hm) Chamber Chamber treated 220 1,310 1,600 1,200 350 79 as 4.8 membrane 2 Treated membrane 0.02 230 280 300 350 500' 91 5.2 6.0

No. l

3 Treated i membrane 008 220 350 90 550 620 96 0.5 5.8 No. 2 l

EXAMPLE l6 ated membrane No. 2. Both were given an equilibrium g property by alternate immersion in 1.0N-HC1 and A 0.02-cm thick polyvinyl chloride sheet was im- 0.5N-NaCl, and their performance as the cation mersed in a mixed solution composed of 90 parts of sty- 20 exchange membranes was measured as in Example 9, rene, 10 parts of 50 percent pure divinylbenzene, 25 with the results shown in Table 15. The treating liquid parts of dioctyl phthalate, 2 parts of benzoylperoxide, employed was 0.05 N-NaCl, the anolyte further conand parts of n-hexane as 'a diluent, for 8 hours. Then taining 300 ppm of a detergent composed mainly of both surfaces of the sheet were covered with cellododecyl pyridinium chloride. In Table 15, Run No. l is phane, and the solution on the sheet was polymerized a control, in which the'cation-exchange membrane prein situ under heating. The filmy product obtained was pared similarly to the other two, except that the Corona treated similarly to Example 14 and the belowdischarge treatment was omitted, was used.

TABLE 15 Type of Quantity Run Ion of Voltage (mV) Variation Current pH of Treated Treating I Effi- Liquid:

No. Exchange Agent 0 4 24. ciency Anode v Cathode Membrane (meq/dm) (min.) (min.) (hrs.) (hrs.) (17) Chamber Chamber I 1 Un- (Y treated r90 890 780 050 76 7.8 4.4 Membrane I 2 Treated i membrane 0.009 230 320 380 480 92 "6.5 5.8

No. l a 3 Treated membrane 0.03 .190 250 280 390 .9l 6.3 6.0 No. 2

specified electrolytes were fixed thereon to form two EXAMPLE 17 types of membranes. i i

Demineralizat on of pulp-treated liquid containing 3 1 percent of acetic acid, 150 ppm of inorganic salts such L LVMIPYIEEE; at}? daubed unifmy m mommy so as of sodium, potassium, calcium, etc., percent of xy- Methanol: SO parts brane surface with absorben lose, and 0.5 percent of lignin sulfonic acid, was at- E-" lii h tempted, using the electrodialysis cell employed in Ex- 2 ample 5. As the cation-exchange membrane, that ob- Polyethyleneiminez 3 parts 1 I tained in Example 3, and as the anion-exchange mema,q'-Azobisisosprayed uniformly onto the j i V bmymnmnez 1 pm membrane surface .55 brane, that obtained in Example 2, were used. The raw Ethanol: parts water of above composition'was caused to flow through a the demineralization chamber in the cell, and 0.2N- NaCl aqueous solution was passed through the concen- The membranes were thoroughly washed with meth- 60 tration chamber, and recycled in the electrodialysis 31101, were Immersed 111 a Solution pq f .1 cell. The electrodialysis was effected for 5 hours at a of at least 90 P P f chlorosulfomc and A constant voltage of 42.5 volts, with the results as shown part of carbon tetrachloride for 2 hours at a C., an in Table: 16, as Run No. 1' Run No 2 is the control in washed thoroughly with carbon tetrachloride. The which the aniomexch n e e bf churned in E membranes were further immersed in 1.0 N-NaOH for a g m m 1 X ample 2 whichwas not surface-treated with sodium 1- amino-B-naphthal-3,fi-disulfonate (untreated .mem-

brane) was used in the similar experiment. In the Control Run, low molecular weight lignin sulfonic acid the membrane. The current efficiency was 82 percent I Also a cation-exchange membrane not treated with polyethyleneimine (untreated membrane) was prepared otlErwisesimilarly to the above procedures. The

in the ControlRun, while it was 92 percent with the 5 'm'eEBrais were tested similarly to li xample l6, with treated membrane of this invention.

the results given in Table 17.

" ""TAB'EE' TI Voltage (mV) Vlrlltlon Current pH of Treated lon- Etflci- Liquids Exchange 30 4 24 ency Anode Cathode Membrane (min.) (ruin.) (hm) (hrs.) (5) Chamber Chamber Treated I I membrane 295 315 330 350 92 6.2 5.9

Untreated membrane 305 850 1210 680 72 8.0 4.2

EXAMPLE 19 TABLE 16' Current Density (A/dm.)

Variation (hrs.) After Demineralization ,.i..... 3 A pasty mixture composed of 95 parts of styrene, 5

parts of divinylbenzene, 100 parts of finely divided polyvinyl chloride, parts of dioctyl phthalate, and 1.5 parts of benzoyl peroxide, was daubed onto a polyvinyl chloride cloth, and allowed to polymerize in situ under heating, to provide a starting cation-exchange membrane.

The membrane'was immersed in a solution composed of 600 g of carbon tetrachloride, g of chloromethyl ether, and 5 g of zinc tetrachloride, at 25C. for 8 hours under stirring, and thereafter thoroughly washed with .methanol. Further the membrane was immersed in a solution composed of 25 mols of phosphorus trichloride and 1.2 mols of 'anh d'rgu's aluminium chloride at room temperature for ours, washed thoroughly with water and immersed in a 5 percent polyethyleneimine aqueous solution at room temperature for 5 hours. As

"a result 0.05 meq/dm of polyethyleneimine was present on the membrane surface. The product was washed with water, immersed in lN-NaOH aqueous solution for 6 hours, and then in lN-l-lCl and phosphorus acid groups were introduced into the membrane (treated A pasty mixture composed of parts of styrene, 90 parts of methyl methacrylate, 20 parts of 50 "percent pure divinylbenzene, 4 parts of benzoyl peroxide, and parts of finely divided polyvinyl chloride, was daubed onto a polyvinyl chloride cloth, and allowed to polymerize in situ at l 10C. for 3 hours, while both surfaces of the cloth were covered with cellophane. The product obtained was immersed in a chloromethylating both composed of 80 parts of carbon tetrachloride, 20 parts of chloromethyl ether, and 3 parts of anhydrous tin tetrachloride, at 25C. for 5 minutes. As a result substantially the surface portion only of the membrane was chloromethylated. The reaction was terminated by placing the membrane in methanol. The membrane was then immersed in the below-specified amino compound for 4 hours to effect substantially surfacial amination reaction, washed thoroughly with methanol, and allowed to dry by standing at room temperature. into the membrane, chlorosulfonic acid groups were introduced as it was immersed in a chlorosulfonating bath composed of 2 parts of chlorosulfonic acid and 1 part of carbon tetrachloride, at 4C. for 3 hours. The chlorosulfonic acid groups were converted to sodium sulfonate, as the membrane was immersed in lN-NaOH at 25C. for 4 hours.

'The membrane was used in electrodialysis effected in acrylic resin-made two-chamber type cell. As the anolyte, 0.04 N-KCl solution containing 100 ppm of dodecyltrimethylammonium chloride, and as the catholyte, 0.04 N-KCl solution, were used. The electrodialysis was carried out at 25.0C., at a current density of 3 mA/cm. The voltage variation after 1,2, and 4 hours of running, current efficiency, and pH of the treated liquids, were measured.

Also the membrane treated as above, except that the aminating treatment after the chloromethylating reaction was omitted, was used as the untreated membrane .mambraney in Control run. The results were shown in Table 18.

TABLE 18 w w k a i Current pH of Treated Voltage (mV) Variation Effici- Liquids Run Treatment Ion-Exchange Membrane 0 l 2 4 ency No. (hr.) (hrs.) (hrs.)

I l Untreated membrane 320 580 650 940 86 8.3 4.0 2 16 Hours immersion in LON-M1 011 330 345 370 390 92 6.4 5.6

TABLE 18 m Current pH of Treated Voltage (mV) Variation Effici- Liquids Run Treatment Ion-Exchange Membrane l 2 4 ency No. (hr.) (hrs) (hrs.) (96) 3 SHohfiirhiiiikih i530 trimethylarnine aqueous solution 325 343" 355 '36s 95 6.2 5.9 4 12 Hours immersion in 5 b polyethyleneimine (molecular 335 340 340 340 98 6.l 5.9

weight; 5,000) 5 8 Hours immersion in S poly- 4-vinylpyridine (molecular 328 330 332 340 97 6 2 6.0

weight: 50,000) solution in alcohol I g g 6 The membrane of Run No. 5 was further immersed for 3 hours 340 340 340 345 98 6.1 6.0

' in 1:1 CH, l -rnethanol solution 7 16 Hours immersion in 5 XI-ethylene diamine aqueous solution 326 340 350 360 94 6.3 5.8

What we claim is: l. A process for the deionization of electrolyte aqueous solutions containing ionic organic matters having a molecular weight of 100 to 300, which consists essentially of disposing cation-exchange membranes and anion-exchange membranes alternately in said electrolyte solutions to thereby form a plurality of chambers con-- sisting of alternating diluting and concentrating chambers by using the disposed cation-exchange and anionexchange membranes as partition walls, each of said ion-exchange membranes consisting of 'an insoluble, infusible synthetic organic polymer having dissociable ionic groups chemically bonded thereto and having the pores across the membranes, at least one substantial surface of each of said ion-exchange membranes intimately retaining an electrolytic substance havingan opposite electric charge to the charge of the ionexchange group of said ion-exchange membrane and being incapable of passing through the pores of the ionexchange membrane, each of said ion-exchange membranes employed as partition wallsbein'g so disposedi face of said ion-exchange membrane, on the basis of "the amount of the dissociable groups of the electrolytic substance. I

3. The process of claim 1, wherein said electrolytic substance has a molecular weight of at least about 400,

J and is intimately retained on the substantial surface by being adsorbed mainly 'by an electrostatic force. 4. The process of claim 1, wherein said electrolytic substance is intimately retained on said substantial sur- 'fyface by being chemically bonded to said substantial surthat it should direct at least said surface intimately re- 7 35 face through a covalent bond. 

2. The process of claim 1, wherein the amount of said electrolytic substance present in said substantial surface is 2 X 10 6 m.eq. to 0.5 m.eq. per dm2 of the surface of said ion-exchange membrane, on the basis of the amount of the dissociable groups of the electrolytic substance.
 3. The process of claim 1, wherein said electrolytic substance has a molecular weight of at least about 400, and is intimately retained on the substantial surface by being adsorbed mainly by an electrostatic force.
 4. The process of claim 1, wherein said electrolytic substance is intimately retained on said substantial surface by being chemically bonded to said substantial surface through a covalent bond. 